A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) associated with a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices promotes chemical reactions in exhaust gas and traps diesel particulate matter (DPM) as exhaust flows through the exhaust system from the engine, thereby preventing significant amounts of pollutants such as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering the atmosphere.
A DPF requires regeneration from time to time in order maintain particulate trapping efficiency. Regeneration involves creating conditions that will burn off trapped particulates whose unchecked accumulation would otherwise impair DPF effectiveness.
The creation of conditions for initiating and continuing regeneration generally involves elevating the temperature of exhaust gas entering the DPF to a suitably high temperature. Because a diesel engine typically runs relatively cool and lean, the post-injection of diesel fuel can be used as part of the strategy to elevate exhaust gas temperatures entering the DPF while still leaving excess oxygen for burning the trapped particulate matter.
When a vehicle is being driven in a way conducive to DPF regeneration, such as at highway speed, the regeneration process may be conducted with little or no significant effect on vehicle driveability, and is typically initiated either automatically by a regeneration initiation strategy. Regeneration occurring under these circumstances may be referred to as “active” regeneration. However, elevation of exhaust gas temperature for initiating “active” DPF regeneration may not always be appropriate for the manner in which a vehicle is being operated.
A related patent filing (Ser. No. 11/711,514) is directed toward a system and method for enhanced “passive” DPF regeneration under circumstances where “active” regeneration may be considered inappropriate. “Passive” regeneration refers to regeneration that results in significantly lower temperature for exhaust gases exiting the DPF than would be the case for “active” regeneration. Consequently, that inventive system and method are considered suitable for DPF regeneration with the engine running while the vehicle is parked.
That invention involves using essentially nitrogen dioxide-based regeneration for passive DPF regeneration instead of the essentially oxygen-based regeneration that characterizes active DPF regeneration. When a vehicle is parked with the engine running, the driver can initiate passive regeneration manually, such as by operating a switch. The engine control system will begin to operate the engine in a way that will force passive regeneration.
When the passive regeneration strategy is invoked, the control system locks out the active regeneration strategy.